Configuring Visual Studio for QT/"Error: Cannot open source file QApplication"

Hi, I am an entry level programmer. My first few programs are already complete, but I still have a lot to learn about tools and frameworks. Currently I am experimenting with QT, making a small application to assist in comparing the units in a game.

So far I have been able to install the plugin and precompiled QT code for Visual studio, and both seems to have been installed correctly. At least QT has taken up it space in the VS menu line, and when I select QT | QT Options | QT Versions, version 4.7.2 shows up as it is presumed that it should.

So far so good (I think). Still, when I load the files given to me by the original developer of the application, I get red lines under my "#include"s, and the error message says

"Error: Cannot open source file QApplication" or more generally put:
"Error: Cannot open source file XXX"

so.. I guess my question is: What is my problem?

Do I need to configure something in:
Project properties (Project | Properties | CC++ Directories)
Include Library, Reference, source or something like that?

Please help the noobs become tomorrows experts :)

Geir

PS! If additonal info is needed, fire freely. I just couldnt think of anything relevant to add.